Surface-modified metal and method for modifying metal surface

ABSTRACT

Provided are surface-modified metals such as metal medical devices, e.g. guide wires, syringe needles, and metal tubes in medical devices or equipment, and methods for modifying a metal surface, wherein a lubricant layer is firmly bonded to the metal surface to impart lubricity to the metal surface and further to improve the durability of the lubricant layer on the metal surface, thereby suppressing deterioration of the sliding properties. Included is a surface-modified metal at least partially having a treated surface, the treated surface being obtained by treating a surface of a metal with a silane coupling agent, followed by adsorbing a hydrogen abstraction type photopolymerization initiator onto the surface and then polymerizing a monomer in the presence of an alkali metal salt.

TECHNICAL FIELD

The present invention relates to surface-modified metals and methods formodifying a metal surface.

BACKGROUND ART

Guide wires and other tools used for assisting insertion of medicaldevices such as catheters into the body are inserted into and optionallyplaced in blood vessels, respiratory tracts, urethra, and other bodycavities or tissues. When a medical device such as a catheter or guidewire is inserted into the body, the medical device may damage the tissueor the like in the body and produce inflammation or cause pain to thepatient. To ameliorate these problems, it has been desired to improvethe sliding properties of the medical devices intended to be insertedinto the body.

To ameliorate the above problems, a method has been proposed in whichthe surface of a medical device such as a catheter or guide wire iscoated with a hydrophilic resin, a fluororesin, or the like.

Moreover, the insertion of a syringe needle into the body may alsodamage the tissue or the like in the body and cause pain to the patient.Furthermore, if the inner surface of a syringe needle, a metal tube in amedical device or equipment, or other metal devices exhibits reducedlubricity when wetted, there may be difficulties in rapidly andaccurately delivering chemicals or blood. Accordingly, it has also beendesired to improve and maintain the lubricity of the inner surface ofthese devices when wetted.

As described above, there have been needs to improve the slidingproperties of medical devices and syringe needles, and to improve andmaintain the lubricity of the inner surface of syringe needles, metaltubes in medical devices or equipment, or other metal devices whenwetted. Various methods have therefore been tried to impart lubricity tothe surface of medical devices such as catheters or guide wires toimprove the sliding properties thereof.

However, all these methods only allow the surface of medical devices tobe coated with a resin or to be cured after the coating. Especially incases where the surface of the medical device is made of a metal, thecoating resin, which is not firmly bonded to the surface of the medicaldevice, is easily peeled or removed from the surface of the medicaldevice, unfortunately resulting in reduction in the sliding propertiesof the medical device. Accordingly, there is a need for the developmentof metal medical devices that exhibit reduced deterioration in slidingproperties. In addition, there is still room for improvement inenhancing and maintaining the lubricity of the inner surface of syringeneedles, metal tubes in medical devices or equipment, or other metaldevices when wetted.

SUMMARY OF INVENTION Technical Problem

The present invention aims to solve the above problems and providesurface-modified metals such as metal medical devices, e.g. guide wires,syringe needles, and metal tubes in medical devices or equipment, andmethods for modifying a metal surface, wherein a lubricant layer isfirmly bonded to the metal surface to impart lubricity to the metalsurface and further to improve the durability of the lubricant layer onthe metal surface, thereby suppressing deterioration of the slidingproperties.

Solution to Problem

The present invention relates to a surface-modified metal, at leastpartially having a treated surface, the treated surface being obtainedby treating a surface of a metal with a silane coupling agent, followedby adsorbing a hydrogen abstraction type photopolymerization initiatoronto the surface and then polymerizing a monomer in the presence of analkali metal salt.

Preferably, the treated surface is obtained by, after adsorbing thehydrogen abstraction type photopolymerization initiator onto the surfaceand then polymerizing the monomer in the presence of the alkali metalsalt, further performing the following step at least once: polymerizinga monomer in the presence of a hydrogen abstraction typephotopolymerization initiator and an alkali metal salt; or adsorbing ahydrogen abstraction type photopolymerization initiator onto the surfaceand then polymerizing a monomer in the presence of an alkali metal salt.

The present invention relates to a surface-modified metal, at leastpartially having a treated surface, the treated surface being obtainedby treating a surface of a metal with a silane coupling agent, followedby polymerizing a monomer in the presence of a hydrogen abstraction typephotopolymerization initiator and an alkali metal salt.

Preferably, the treated surface is obtained by, after polymerizing themonomer in the presence of the hydrogen abstraction typephotopolymerization initiator and the alkali metal salt, furtherperforming the following step at least once: polymerizing a monomer inthe presence of a hydrogen abstraction type photopolymerizationinitiator and an alkali metal salt; or adsorbing a hydrogen abstractiontype photopolymerization initiator onto the surface and thenpolymerizing a monomer in the presence of an alkali metal salt.

The monomer is preferably at least one selected from the groupconsisting of hydrophilic monomers, alkali metal-containing monomers,and halogen-containing monomers.

The silane coupling agent is preferably a vinyl group-containingcompound.

The metal to be treated is preferably stainless steel or anickel-titanium alloy.

The present invention relates to a medical device, including thesurface-modified metal.

The medical device is preferably a guide wire, a syringe needle, or atube of a medical instrument.

The present invention relates to a method for modifying a metal surface,the method including:

step 1 of treating a metal surface with a silane coupling agent;

step 2 of adsorbing a hydrogen abstraction type photopolymerizationinitiator onto the metal surface treated in the step 1 to formpolymerization initiation points; and

step 3 of polymerizing a monomer starting from the polymerizationinitiation points in the presence of an alkali metal salt to growpolymer chains on the metal surface.

The present invention relates to a method for modifying a metal surface,the method including:

step I of treating a metal surface with a silane coupling agent; and

step II of polymerizing a monomer in the presence of a hydrogenabstraction type photopolymerization initiator and an alkali metal salton the metal surface treated in the step I to grow polymer chains on themetal surface.

Preferably, after the step 3 or the step II, the method for modifying ametal surface includes performing, at least once: a step of adsorbing ahydrogen abstraction type photopolymerization initiator onto the surfaceand then polymerizing a monomer in the presence of an alkali metal salt;or a step of polymerizing a monomer in the presence of a hydrogenabstraction type photopolymerization initiator and an alkali metal salt.

Advantageous Effects of Invention

The surface-modified metals of the present invention are characterizedby at least partially having a treated surface obtained by treating thesurface of metals with a silane coupling agent, followed by adsorbing ahydrogen abstraction type photopolymerization initiator onto the surfaceand then polymerizing a monomer in the presence of an alkali metal salt;or a treated surface obtained by treating the surface of metals with asilane coupling agent, followed by polymerizing a monomer in thepresence of a hydrogen abstraction type photopolymerization initiatorand an alkali metal salt. Such surface-modified metals have lubricityimparted to the metal surface, and further have improved durability ofthe lubricant layer on the surface and therefore reduced deteriorationin the sliding properties of the metal. In addition, the efficiency ofthe polymerization is improved. These effects are presumably produced bythe presence of a hydrogen abstraction type photopolymerizationinitiator that allows a polymer derived from a monomer to be chemicallybonded to the metal surface, and an alkali metal salt that promotes thepolymerization so that the polymerization can be completed in a shortertime.

DESCRIPTION OF EMBODIMENTS

The first surface-modified metal of the present invention ischaracterized by at least partially having a treated surface obtained bytreating the surface of a metal with a silane coupling agent, followedby adsorbing a hydrogen abstraction type photopolymerization initiatoronto the surface and then polymerizing a monomer in the presence of analkali metal salt.

Lubricant layers formed on metal surfaces by conventional surfacetreatment or coating methods are not chemically bonded to the metalsurfaces and are easily peeled or removed by a stress such as rubbing bya hand, friction with an object contacting the metal (e.g., a catheteror cells in the body when the metal is a guide wire), flows of chemicalsor blood, or other causes. Such lubricant layers are thereforedisadvantageous in terms of durability or maintaining slidingproperties. In contrast, the surface-modified metal of the presentinvention is obtained by polymerizing a monomer in the presence of ahydrogen abstraction type photopolymerization initiator and an alkalimetal salt which allow a polymer derived from the monomer to bechemically bonded to the metal surface and, further, promote thepolymerization rate. Thus, a lubricant layer is formed by the efficientsurface treatment, and further the formed lubricant layer is inhibitedfrom being peeled or removed by a stress, friction, liquid flows, orother causes and thus deterioration in the sliding properties of themetal is prevented.

The surface-modified metal of the present invention may be prepared by,for example, a method for modifying a metal surface which includes: step1 of treating a metal surface with a silane coupling agent; step 2 ofadsorbing a hydrogen abstraction type photopolymerization initiator ontothe metal surface treated in the step 1 to form polymerizationinitiation points; and step 3 of polymerizing a monomer starting fromthe polymerization initiation points in the presence of an alkali metalsalt to grow polymer chains on the metal surface.

By the treatment with a silane coupling agent before the polymerizationof a monomer in the presence of a hydrogen abstraction typephotopolymerization initiator and an alkali metal salt, the polymer ischemically bonded to the metal via the silane coupling agent so that astronger bond is formed. Thus, the surface-modified metal has furtherenhanced and more durable sliding properties.

Examples of the metal include, but are not limited to, stainless steel,nickel-titanium alloys, iron, titanium, aluminum, tin, and zinc-tungstenalloys. Among these, stainless steel or nickel-titanium alloys arepreferred in view of bonding between the metal surface and the lubricantlayer and biocompatibility.

The silane coupling agent may suitably be a vinyl group-containingcompound. For example, for easy hydrogen abstraction, the vinylgroup-containing compound preferably contains a hydrolyzable group and avinyl group. Such a vinyl group-containing compound reacts with andbonds to the hydroxy group on the metal surface via the hydrolyzablegroup, and its vinyl group can form a polymerization initiation pointfor monomers. Consequently, polymer chains grown starting from thepolymerization initiation points are chemically bonded to the metal viathe silane coupling agent.

Preferred as the silane coupling agent are vinyltrimethoxysilane,vinyltriethoxysilane, (3-acryloyloxypropyl)trimethoxysilane,(3-acryloyloxypropyl)triethoxysilane,(3-methacryloyloxypropyl)trimethoxysilane,(3-methacryloyloxypropyl)triethoxysilane, vinylchlorodimethylsilane,(3-acryloyloxypropyl)chlorodimethylsilane, and(3-methacryloyloxypropyl)chlorodimethylsilane. More preferred are(3-acryloyloxypropyl)trimethoxysilane,(3-acryloyloxypropyl)triethoxysilane, and(3-acryloyloxypropyl)chlorodimethylsilane. In view of reactivity orsafety, particularly preferred is (3-acryloyloxypropyl)trimethoxysilane.

The treatment with the silane coupling agent may be carried out by anymethod that allows the silane coupling agent to be brought into contactwith the metal, such as by coating it by for example application,spraying, or immersion. The treatment is preferably carried out bypreparing a solution (e.g. an aqueous solution, alcohol solution, oracetone solution) of a silane coupling agent (silane compound), andcoating the metal surface with the solution, followed either by dryingby heat, or by standing under air moisture, wet or other conditions tocause hydrolysis and dehydration condensation. According to thesemethods, a chemical bond is formed between the hydroxy group on themetal surface and the silane coupling agent (silane compound) so thatthe silane coupling agent is fixed. The drying temperature and dryingtime may be selected appropriately, for example, to allow formation of achemical bond. The drying temperature is preferably 40° C. to 150° C. Inthe preparation of the aqueous solution, an additional operation may beperformed as appropriate, for example, by adding alcohol to prepare amixed water/alcohol solution or by adjusting the pH to weakly acidicwith acetic acid or other acids. This is because the solubility of thesilane coupling agent in water varies depending on the type of silanecoupling agent.

The formation of polymerization initiation points in step 2 may becarried out, for example, by adsorbing a hydrogen abstraction typephotopolymerization initiator onto the metal surface treated with asilane coupling agent in step 1, to form polymerization initiationpoints, or by adsorbing a hydrogen abstraction type photopolymerizationinitiator onto the metal surface treated with a silane coupling agentand then irradiating the surface with ultraviolet light having awavelength of 300 to 400 nm to form polymerization initiation pointsfrom the hydrogen abstraction type photopolymerization initiator on thesurface.

Examples of the hydrogen abstraction type photopolymerization initiatorinclude carbonyl compounds, organic sulfur compounds such astetraethylthiuram disulfide, persulfides, redox compounds, azocompounds, diazo compounds, halogen compounds, and photoreducing dyes.Preferred among these are carbonyl compounds.

The carbonyl compound used as a hydrogen abstraction typephotopolymerization initiator is preferably benzophenone or a derivativethereof (a benzophenone compound). For example, it may suitably be abenzophenone compound represented by the following formula:

wherein R¹ to R⁵ and R¹′ to R⁵′ are the same as or different from oneanother and each represent a hydrogen atom, an alkyl group, a halogen(fluorine, chlorine, bromine, or iodine), a hydroxy group, a primary,secondary, or tertiary amino group, a mercapto group, or a hydrocarbongroup that may contain an oxygen, nitrogen, or sulfur atom, and any twoadjacent groups of R¹ to R⁵ and R¹′ to R⁵′ may be joined to each otherto form a ring together with the carbon atoms to which they areattached.

Specific examples of the benzophenone compound include benzophenone,xanthone, 9-fluorenone, 2,4-dichlorobenzophenone, methylo-benzoylbenzoate, 4,4′-bis(dimethylamino)benzophenone, and4,4′-bis(diethylamino)benzophenone. Particularly preferred among theseare benzophenone, xanthone, and 9-fluorenone as these compoundscontribute to forming polymer brushes well.

The hydrogen abstraction type photopolymerization initiator may alsosuitably be a thioxanthone compound because it provides a highpolymerization rate and because of its ease of adsorption and/orreaction. For example, it may suitably be a compound represented by thefollowing formula:

wherein R⁶ to R⁹ and R⁶′ to R⁹′ are the same as or different from oneanother and each represent a hydrogen atom, a halogen atom, or an alkyl,cyclic alkyl, aryl, alkenyl, alkoxy, or aryloxy group.

Examples of the thioxanthone compound represented by the above formulainclude thioxanthone, 2-isopropylthioxanthone, 4-isopropylthioxanthone,2,3-diethylthioxanthone, 2,4-diethylthioxanthone,2,4-dichlorothioxanthone, 2-methoxythioxanthone,l-chloro-4-propoxythioxanthone, 2-cyclohexylthioxanthone,4-cyclohexylthioxanthone, 2-vinylthioxanthone, 2,4-divinylthioxanthone,2,4-diphenylthioxanthone, 2-butenyl-4-phenylthioxanthone, and2-p-octyloxyphenyl-4-ethylthioxanthone. Preferred among these are thosewhich are substituted at one or two, especially two, of R⁶ to R⁹ and R⁶′to R⁹′ with alkyl groups. More preferred is 2,4-diethylthioxanthone.

The adsorption of a hydrogen abstraction type photopolymerizationinitiator such as a benzophenone or thioxanthone compound onto the metalsurface may be carried out as follows. In the case of a benzophenone orthioxanthone compound, for example, the benzophenone or thioxanthonecompound is dissolved in an organic solvent to prepare a solution; asurface portion of the metal to be modified is treated with thissolution so that the compound is adsorbed on the surface portion; and,if necessary, the organic solvent is dried and evaporated off, wherebypolymerization initiation points are formed. The surface-treating methodmay be any method that allows the solution of the benzophenone orthioxanthone compound to be brought into contact with the metal surfacetreated with a silane coupling agent. Suitable methods include applyingor spraying the benzophenone or thioxanthone compound solution onto thesurface; or immersing the surface into the solution. When only a part ofthe surface needs to be modified, it is sufficient to adsorb thehydrogen abstraction type photopolymerization initiator only onto thenecessary part of the surface. In this case, for example, application orspraying of the solution is suitable. Examples of the solvent includemethanol, ethanol, acetone, benzene, toluene, methyl ethyl ketone, ethylacetate, and THF. Preferred is acetone because it dries and evaporatesquickly.

As described above, after a hydrogen abstraction typephotopolymerization initiator is adsorbed on the metal surface treatedwith a silane coupling agent, the metal surface may further beirradiated with ultraviolet light having a wavelength of 300 to 400 nmto form polymerization initiation points from the hydrogen abstractiontype photopolymerization initiator on the surface. This ultravioletirradiation may be carried out by known methods. For example, theultraviolet irradiation may be carried out in the same manner asdescribed later. In the adsorption of the photopolymerization initiatorand the fixation thereof by ultraviolet irradiation (chemical bondformation), hydrogen is abstracted from the hydroxy group on the metalsurface and the resulting hydroxy group on the metal surface iscovalently bonded to the carbon of C═O in the benzophenone orthioxanthone compound while the abstracted hydrogen is bonded to theoxygen of C═O to form C—O—H.

Step 3 may be carried out, for example, by radically polymerizing amonomer starting from the polymerization initiation points formed instep 2, by irradiation with ultraviolet light having a wavelength of 300to 400 nm in the presence of an alkali metal salt to grow polymer chainson the metal surface. In particular, by carrying out step 3 in thepresence of an alkali metal salt, the polymer is sufficiently fixed tothe metal surface, and therefore excellent lubricity and excellentlubricant durability are imparted to the metal surface.

Examples of alkali metal salts that can be used include halogenatedalkali metal salts, alkali metal carbonates, alkali metal bicarbonates,alkali metal hydrogen carbonates, alkali metal nitrates, alkali metalsulfates, alkali metal bisulfates, alkali metal phosphates, alkali metalhydroxides, alkali metal acetates, alkali metal citrates, and alkalimetal lactates. The alkali metal salt may be a water-soluble lithium,sodium, potassium, rubidium, or cesium salt.

Specific examples include sodium chloride, potassium chloride, cesiumchloride, sodium bromide, potassium bromide, sodium nitrate, potassiumnitrate, sodium carbonate, potassium carbonate, sodium sulfate,potassium sulfate, sodium bisulfate, potassium bisulfate, sodiumphosphate, potassium phosphate, sodium hydroxide, potassium hydroxide,sodium hydrogen carbonate, sodium dihydrogen phosphate, disodiumhydrogen phosphate, trisodium phosphate, sodium acetate, potassiumacetate, sodium citrate, potassium citrate, sodium lactate, andpotassium lactate. The alkali metal salts may be used alone or incombinations of two or more.

In view of lubricity and lubricant durability, halogenated alkali metalsalts are preferred among these, and sodium chloride or potassiumchloride is particularly preferred.

Suitable examples of the monomer include hydrophilic monomers, alkalimetal-containing monomers (monomers each containing an alkali metal inthe molecule), zwitterionic monomers (zwitterionic group-containingcompounds: compounds each bearing a center of permanent positive chargeand a center of negative charge), and halogen-containing monomers(monomers each containing a halogen in the molecule). If monomerssimultaneously correspond to two or more of the above types of monomers,i.e. hydrophilic monomers, alkali metal-containing monomers,zwitterionic monomers, and halogen-containing monomers, as in the caseof, for example, a monomer containing an alkali metal and a halogen(corresponding to both the alkali metal-containing monomer type and thehalogen-containing monomer type), they are included in any of the two ormore monomer types. The monomers may be used alone or in combinations oftwo or more.

The hydrophilic monomer may be a monomer containing a functional groupthat can be converted to a hydrophilic functional group, and examplesinclude monomers containing hydrophilic groups, such as typically anamide group, a sulfuric acid group, a sulfonic acid group, a carboxylicacid group, a hydroxy group, an amino group, an oxyethylene group, orprecursor functional groups of these groups.

Specific examples of the hydrophilic monomer include (meth)acrylic acid,(meth)acrylic acid esters such as methoxyethyl (meth)acrylate andhydroxyethyl (meth)acrylate, alkali metal salts of (meth)acrylic acid,and amine salts of (meth)acrylic acid. Monomers containing a C—N bond inthe molecule may also be mentioned. Examples of the monomer containing aC—N bond in the molecule include (meth) acrylamide; N-alkyl-substituted(meth)acrylamide derivatives such as N-ethyl(meth)acrylamide,N-n-propyl(meth)acrylamide, N-isopropyl(meth)acrylamide,N-cyclopropyl(meth)acrylamide, N-methoxyethyl(meth)acrylamide, andN-ethoxyethyl(meth)acrylamide; N,N-dialkyl-substituted (meth)acrylamidederivatives such as N,N-dimethyl(meth)acrylamide,N,N-ethylmethyl(meth)acrylamide, and N,N-diethyl(meth)acrylamide;hydroxy(meth)acrylamide; hydroxy(meth)acrylamide derivatives such asN-hydroxyethyl(meth)acrylamide; and cyclic group-containing(meth)acrylamide derivatives such as (meth)acryloylmorpholine. Preferredamong these are (meth)acrylic acid, (meth)acrylic acid esters, alkalimetal salts of (meth)acrylic acid, amine salts of (meth)acrylic acid,acrylonitrile, (meth)acrylamide, dimethyl(meth)acrylamide,diethyl(meth)acrylamide, isopropyl(meth)acrylamide,hydroxyethyl(meth)acrylamide, methoxyethyl(meth)acrylamide, and(meth)acryloylmorpholine. More preferred is (meth) acrylamide or2-methoxyethyl acrylate, with 2-methoxyethyl acrylate being particularlypreferred.

Examples of the alkali metal-containing monomer include alkali metalsalts of acrylic acid such as sodium acrylate and potassium acrylate;alkali metal salts of methacrylic acid such as sodium methacrylate andpotassium methacrylate; alkali metal salts of itaconic acid such assodium itaconate and potassium itaconate; alkali metal salts of3-vinylpropionic acid such as sodium 3-vinylpropionate and potassium3-vinylpropionate; alkali metal salts of vinylsulfonic acid such assodium vinylsulfonate and potassium vinylsulfonate; alkali metal saltsof 2-sulfoethyl (meth)acrylate such as sodium 2-sulfoethyl(meth)acrylate and potassium 2-sulfoethyl (meth)acrylate; alkali metalsalts of 3-sulfopropyl (meth) acrylate such as sodium 3-sulfopropyl(meth) acrylate and potassium 3-sulfopropyl (meth)acrylate; alkali metalsalts of 2-acrylamide-2-methylpropanesulfonic acid such as sodium2-acrylamide-2-methylpropanesulfonate and potassium2-acrylamide-2-methylpropanesulfonate; and alkali metal salts ofstyrenesulfonic acid such as sodium styrenesulfonate and potassiumstyrenesulfonate. Preferred among these is potassium 3-sulfopropylmethacrylate.

Examples of the zwitterionic monomer include carboxybetaines,sulfobetaines, and phosphobetaines. Other examples include compoundsrepresented by the formula (1) below, suitably compounds represented bythe formula (2) below.

In the formula, R¹¹ represents —H or —CH₃; X represents —O—, —NH— or—N⁺—; m represents an integer of 1 or more; and Y represents azwitterionic group or a halogen group such as Cl⁻, Br⁻, or F⁻.

In the formula (1), preferably, R¹¹ is —CH₃, X is —O—, and m is aninteger of 1 to 10. In the zwitterionic group designated by Y, thecation may be a quaternary ammonium such as tetraalkylammonium, and theanion may be a carboxylate, sulfonate, or phosphate.

In the formula, R¹¹ represents —H or —CH₃; p and q each represent aninteger of 1 or more; and Y¹ and Y² represent ionic functional groupshaving electric charges opposite to each other.

In the formula (2), p is preferably an integer of 2 or larger, morepreferably an integer of 2 to 10, and q is preferably an integer of 1 to10, more preferably an integer of 2 to 4. Preferred examples of R¹¹ arethe same as mentioned above. The symbols Y¹ and Y² are as described forthe cation and anion above.

Typical suitable examples of the zwitterionic monomer include compoundsrepresented by the following formulas (2-1) to (2-4):

wherein R¹¹ represents a hydrogen atom or a methyl group, and p and qeach represent an integer of 1 to 10,

p and q each represent an integer of 1 to 10,

wherein R¹¹ represents a hydrogen atom or a methyl group; R¹² representsa C1-C6 hydrocarbon group; and p and q each represent an integer of 1 to10,

wherein R¹¹ represents a hydrogen atom or a methyl group; R¹³, R¹⁴, andR¹⁵ are the same as or different from one another and each represent aC1-C2 hydrocarbon group; and p and q each represent an integer of 1 to10.

Examples of compounds represented by the formula (2-1) includedimethyl(3-sulfopropyl) (2-(meth)acryloyloxyethyl)-ammonium betaine and[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)aminium hydroxide.Examples of compounds represented by the formula (2-2) includedimethyl(2-carboxyethyl) (2-(meth)acryloyloxyethyl)ammonium betaine.Examples of compounds represented by the formula (2-3) includedimethyl(3-methoxyphosphopropyl)-(2-(meth)acryloyloxyethyl)ammoniumbetaine. Examples of compounds represented by the formula (2-4) include2-(meth)acryloyloxyethyl phosphorylcholine. Other zwitterionic monomersinclude 2-(meth)acryloyloxyethyl carboxybetaine and2-(meth)acryloyloxyethyl sulfobetaine. Preferred among these is2-(meth)acryloyloxyethyl phosphorylcholine because of its highbiocompatibility, i.e. low protein adsorbability.

The halogen-containing monomer refers to a hydrophilic monomercontaining a halogen atom in the molecule. The halogen-containingmonomers may be used alone or in combinations of two or more.

In view of lubricity and lubricant durability, the halogen-containingmonomer may suitably be a nitrogen-containing monomer (halogen- andnitrogen-containing monomer). Specific preferred examples of suchmonomers include compounds represented by the following formula (I):

wherein A represents an oxygen atom or NH; B represents a C1-C4 alkylenegroup; R¹⁰¹ represents a hydrogen atom or a methyl group; R¹⁰², R¹⁰³,and R¹⁰⁴ are the same as or different from one another and eachrepresent a C1-C4 alkyl group; and X⁻ represents a halogen ion.

The symbol A is preferably an oxygen atom. The symbol B may be a linearor branched alkylene group such as a methylene group, an ethylene group,or a propylene group, with a methylene group or an ethylene group beingpreferred. Each of R¹⁰² to R¹⁰⁴ may be a linear or branched alkyl groupsuch as a methyl group, an ethyl group, or a propyl group, with a methylgroup or an ethyl group being preferred. The symbol X (halogen atom) maybe, for example, fluorine, chlorine, or bromine, preferably chlorine.

Examples of nitrogen-containing monomers represented by the formula (I)include 2-(methacroyloxy)ethyl trimethylammonium chloride(2-(methacroyloxy)ethyl trimethylaminium chloride), 2-(acryloyloxy)ethyltrimethylammonium chloride (2-(acryloyloxy)ethyl trimethylaminiumchloride), 2-(methacroyloxy)ethyl dimethylethylammonium chloride(2-(methacroyloxy)ethyl dimethylethylaminium chloride), and2-(acryloyloxy)ethyl dimethylethylammonium chloride(2-(acryloyloxy)ethyl dimethylethylaminium chloride).

The radical polymerization of a monomer in step 3 is carried out, forexample, as follows: a solution of an alkali metal salt and a monomer ora mixture of an alkali metal salt and a liquid monomer is applied(sprayed) onto the silane coupling agent-treated metal surface on whicha benzophenone or thioxanthone compound or the like has been adsorbed,or the silane coupling agent-treated metal is immersed in a solution ofan alkali metal salt and a monomer or a mixture of an alkali metal saltand a liquid monomer; and then the metal surface is irradiated withultraviolet light to allow radical polymerization (photoradicalpolymerization) of the monomer to proceed, whereby polymer chains aregrown on the metal surface. After the application, the metal surface mayfurther be covered with a transparent cover of glass, PET, polycarbonateor other materials, followed by irradiating the covered surface withlight (e.g. ultraviolet light) to allow radical polymerization(photoradical polymerization) of the monomer to proceed, whereby polymerchains are grown on the metal surface.

The solvent for application (spraying), the method for application(spraying), the method for immersion, the conditions for irradiation,and the like may be conventionally known materials or methods. Thesolution of the radically polymerizable monomer may be an aqueoussolution, or a solution in an organic solvent that does not dissolve thehydrogen abstraction type photopolymerization initiator used (e.g. abenzophenone or thioxanthone compound). Moreover, the solution of theradically polymerizable monomer or the liquid radically polymerizablemonomer may contain a known polymerization inhibitor such as4-methylphenol.

In the present invention, the radical polymerization of the monomer isallowed to proceed by light irradiation after the application of themonomer solution or the liquid monomer, or after the immersion in themonomer solution or the liquid monomer. In the light irradiation,ultraviolet light sources with an emission wavelength mainly in theultraviolet region, such as high-pressure mercury lamps, metal halidelamps, and LED lamps, can be suitably used. The light dose may beselected appropriately in view of polymerization time and uniformprogress of the reaction. Moreover, in order to prevent inhibition ofpolymerization due to active gas such as oxygen in the reaction vesseland the reaction pipe, oxygen is preferably removed from the reactionvessel, the reaction pipe, and the reaction solution during or beforethe light irradiation. To this end, appropriate operations may beperformed; for example, an inert gas such as nitrogen gas or argon gasis introduced into the reaction vessel, the reaction pipe, and thereaction solution to discharge active gas such as oxygen from thereaction system and replace the atmosphere in the reaction system withthe inert gas. Furthermore, in order to prevent inhibition of thereaction due to oxygen and the like, for example, a measure may alsoappropriately be taken in which an ultraviolet light source is placedsuch that an air layer (oxygen content: 15% or higher) does not existbetween the reaction vessel made of glass, plastic or the like and thereaction solution or the object intended to be modified.

The ultraviolet light preferably has a wavelength of 300 to 400 nm. Sucha wavelength enables polymer chains to be formed well on the metalsurface. Examples of light sources that can be used includehigh-pressure mercury lamps, LEDs with a center wavelength of 365 nm,LEDs with a center wavelength of 375 nm, and LEDs with a centerwavelength of 385 nm. More preferred is irradiation with LED lighthaving a wavelength of 355 to 390 nm. In particular, for example, LEDswith a center wavelength of 365 nm, which is close to the excitationwavelength (366 nm) of benzophenone, are preferred in view ofefficiency. Light having a wavelength of less than 300 nm can cleave anddamage molecules of the object intended to be modified. For this reason,light having a wavelength of 300 nm or greater is preferred. Morepreferred is light having a wavelength of 355 nm or greater because itproduces very little damage to the metal. In contrast, light having awavelength of greater than 400 nm is less likely to activate thephotopolymerization initiator, so that the polymerization reaction doesnot readily proceed. For this reason, light having a wavelength of 400nm or less is preferred. Although LED light is suitable because thewavelength range of LED light is narrow so that no wavelengths otherthan the center wavelength are emitted, a mercury lamp or the like canalso achieve similar effects to those of LED light if a filter is usedto block light with wavelengths less than 300 nm.

In the present invention, polymer chains can be produced with goodproductivity by reducing the duration of irradiation with ultravioletlight having a wavelength of, for example, 300 to 400 nm. For example,when polymer chains are formed on a metal plate, the duration of lightirradiation for one polymer chain forming step may be 3 to 120 minutes,and can also be reduced to 5 to 100 minutes, or 10 to 80 minutes. Whenpolymer chains are formed on a guide wire, the duration of lightirradiation for one polymer chain forming step may be 10 to 1,000minutes, and can also be reduced to 60 to 800 minutes, or 100 to 600minutes.

The second surface-modified metal of the present invention ischaracterized by at least partially having a treated surface obtained bytreating the surface of a metal with a silane coupling agent, followedby polymerizing a monomer in the presence of a hydrogen abstraction typephotopolymerization initiator and an alkali metal salt. Such asurface-modified metal may be prepared by, for example, a method formodifying a metal surface which includes: step I of treating a metalsurface with a silane coupling agent; and step II of polymerizing amonomer in the presence of a hydrogen abstraction typephotopolymerization initiator and an alkali metal salt on the metalsurface treated in the step I to grow polymer chains on the metalsurface. By radically polymerizing a monomer in the presence of ahydrogen abstraction type photopolymerization initiator as an initiatorand further an alkali metal salt to produce polymer chains, asurface-modified metal can be produced on which a polymer layer(polymer) is fixed to the metal surface. Thus, similarly to the above, alubricant layer is formed by the efficient surface treatment, andfurther the formed lubricant layer is inhibited from being peeled orremoved by a stress, friction, liquid flows, or other causes and thusdeterioration in the sliding properties of the metal is prevented. Themetal, the silane coupling agent, the hydrogen abstraction typephotopolymerization initiator, the alkali metal salt, and the monomerused in step I may be the same as those described above.

The treatment with a silane coupling agent in step I may be carried outin the same manner as in step 1.

Step II may be carried out, for example, by bringing the metal surfacetreated with a silane coupling agent into contact with a hydrogenabstraction type photopolymerization initiator, an alkali metal salt,and a monomer, followed by irradiating the metal surface with LED lighthaving a wavelength of 300 to 400 nm to form polymerization initiationpoints from the photopolymerization initiator while radicallypolymerizing the monomer starting from the polymerization initiationpoints in the presence of the alkali metal salt to grow polymer chains.

The radical polymerization of a monomer in step II may be carried out asfollows: a solution of a monomer or a liquid monomer which contains ahydrogen abstraction type photopolymerization initiator such as abenzophenone or thioxanthone compound and an alkali metal salt isapplied (sprayed) onto the metal surface treated with a silane couplingagent, or the metal surface treated with a silane coupling agent isimmersed in a solution of a monomer or a liquid monomer which contains ahydrogen abstraction type photopolymerization initiator and an alkalimetal salt; and then the metal surface is irradiated with light (e.g.ultraviolet light) to allow radical polymerization (photoradicalpolymerization) of the monomer to proceed, whereby polymer chains aregrown on the metal surface. Further, the metal surface may be coveredwith a transparent cover of glass, PET, polycarbonate or othermaterials, followed by irradiating the covered surface with light (e.g.ultraviolet light) as described hereinabove. The solvent for application(spraying), the method for application (spraying), the method forimmersion, the conditions for irradiation, and the like may be thematerials or methods described hereinabove. Moreover, similarly to theabove, when polymer chains are formed on a metal plate, the duration ofirradiation with ultraviolet light having a wavelength of, for example,300 to 400 nm for one polymer chain forming step may be reduced to 3 to120 minutes, 5 to 100 minutes, or 10 to 80 minutes. When polymer chainsare formed on a guide wire, the duration of light irradiation for onepolymer chain forming step may be reduced to 10 to 1000 minutes, 60 to800 minutes, or 100 to 600 minutes.

In step 3 and step II, two or more types of monomers may be radicallypolymerized simultaneously. Moreover, multiple types of polymer chainsmay be grown on the metal surface. Furthermore, the polymer chains maybe cross-linked to one another. In this case, the polymer chains may becrosslinked to one another by ionic crosslinking, crosslinking by ahydrophilic group containing an oxygen atom, or crosslinking by ahalogen group such as iodine.

After step 3 or step II, the methods may include performing, at leastonce: a step of adsorbing a hydrogen abstraction typephotopolymerization initiator onto the surface and then polymerizing amonomer in the presence of an alkali metal salt; or a step ofpolymerizing a monomer in the presence of a hydrogen abstraction typephotopolymerization initiator and an alkali metal salt. Each step may becarried out in the same manner as in, for example, step 2, step 3, orstep II.

The above-described modification methods may be applied to at least apart of a three-dimensional solid body to produce a surface-modifiedthree-dimensional metal with modified properties. Preferred examplesinclude polymer brushes. The term “polymer brush” means an assembly ofgraft polymer molecules obtained in the “grafting from” approach bysurface-initiated polymerization. The graft chains are preferablyoriented in a direction substantially vertical to the surface of themodified object because then the entropy decreases to reduce themolecular mobility of the graft chains, thereby providing lubricity.Furthermore, semidilute or concentrated brushes having a brush densityof 0.01 chains/nm² or higher are preferred.

The surface modification methods may be used to produce medical devicesat least partially having a modified surface. The modification ispreferably applied to the surface of medical devices at least at aportion that requires lubricity, and may be applied to the entiresurface.

The surface-modified metals of the present invention have lubricityimparted to the metal surface, and further have improved durability ofthe lubricant layer on the metal surface and therefore reduceddeterioration in the sliding properties of the metal. Suchsurface-modified metals can be suitably used for, for example, metalmedical devices, e.g. guide wires, syringe needles, metal tubes inmedical devices or equipment, and other medical devices.

EXAMPLES

The present invention is more specifically described with reference toexamples below, but is not limited only to these examples.

Example 1

The surface of a SUS flat plate (10 cm square, 1 mm in thickness) waswashed with acetone and dried.

The plate was immersed in a 2% by mass aqueous solution of(3-acryloyloxypropyl)trimethoxysilane containing 2% by mass of aceticacid for 10 minutes, taken out and dried for 24 hours. The plate wasthen washed with acetone. The treated SUS plate was immersed in a 1% bymass solution of benzophenone in acetone, taken out and dried.

On the surface of the dried SUS plate was dropped an aqueous solution of2-(methacroyloxy) ethyl trimethylammonium chloride (1.25 M) containingsodium chloride adjusted at a concentration of 1.5 M. Then, the surfacewas covered with a 1 mm thick glass plate, and the covered surface wasirradiated with LED-UV (5 mW/cm²) having a wavelength of 365 nm for 60minutes to cause surface-initiated radical polymerization. Subsequently,the surface was washed with water to wash away unreacted monomer and thelike. In this manner, a surface-modified metal was prepared.

Example 2

The surface of a SUS flat plate (10 cm square, 1 mm in thickness) waswashed with acetone and dried.

The plate was immersed in a 2% by mass aqueous solution of(3-acryloyloxypropyl)trimethoxysilane containing 2% by mass of aceticacid for 10 minutes, taken out and dried for 24 hours. The plate wasthen washed with acetone. The treated SUS plate was immersed in a 1% bymass solution of benzophenone in acetone, taken out and dried.

On the surface of the dried SUS plate was dropped an aqueous solution of2-(methacroyloxy)ethyl trimethylammonium chloride (1.25 M) containingpotassium chloride adjusted at a concentration of 0.75 M. Then, thesurface was covered with a 1 mm thick glass plate, and the coveredsurface was irradiated with LED-UV (5 mW/cm²) having a wavelength of 365nm for 60 minutes to cause surface-initiated radical polymerization.Subsequently, the surface was washed with water to wash away unreactedmonomer and the like. In this manner, a surface-modified metal wasprepared.

Example 3

The treatment with a silane coupling agent, benzophenone treatment, anddrying were carried out in the same manner as in Example 1, except thatthe SUS plate was changed to a SUS guide wire (core wire).

Subsequently, the dried guide wire was put in a glass vessel containingan aqueous solution of 2-(methacroyloxy)ethyl trimethylammonium chloride(1.25 M) containing sodium chloride adjusted at a concentration of 1.5M, and the vessel was sealed with a stopper. After argon substitutionwas performed for two hours to remove oxygen, the glass vessel wasirradiated with LED-UV (5 mW/cm²) for 480 minutes while being rotated,to cause surface-initiated radical polymerization. In this manner, asurface-modified metal was prepared.

Example 4

A surface-modified metal was prepared by carrying out surface-initiatedradical polymerization in the same manner as in Example 3, except thatthe SUS guide wire (core wire) was changed to a nickel-titanium alloyguide wire.

Example 5

The surface of a SUS guide wire (core wire) was washed with acetone anddried.

The guide wire was immersed in a 2% by mass aqueous solution of(3-acryloyloxypropyl)trimethoxysilane containing 2% by mass of aceticacid for 10 minutes, taken out and dried for 24 hours. The guide wirewas then washed with acetone. The treated SUS guide wire was immersed ina 1% by mass solution of benzophenone in acetone, taken out and dried.

The dried SUS guide wire was put in a glass vessel containing an aqueoussolution containing acrylic acid and sodium chloride adjusted atconcentrations of 2.5 M and 1.5 M, respectively, and the vessel wassealed with a stopper. After argon substitution was performed for twohours to remove oxygen, the glass vessel was irradiated with LED-UV (5mW/cm²) having a wavelength of 365 nm for 480 minutes while beingrotated, to cause surface-initiated radical polymerization.

Subsequently, the surface was washed with water and dried, and then theguide wire was immersed in a 1% by mass solution of benzophenone inacetone, taken out and dried.

The dried guide wire was put in a glass vessel containing an aqueoussolution of 2-(methacroyloxy)ethyl trimethylammonium chloride (1.25 M)containing sodium chloride adjusted at a concentration of 1.5 M, and thevessel was sealed with a stopper. After argon substitution was performedfor two hours to remove oxygen, the glass vessel was irradiated withLED-UV (5 mW/cm²) having a wavelength of 365 nm for 480 minutes whilebeing rotated, to cause surface-initiated radical polymerization.Subsequently, the surface was washed with water to wash away unreactedmonomer and the like. In this manner, a surface-modified metal wasprepared.

Example 6

The surface of a SUS guide wire (core wire) was washed with acetone anddried.

The guide wire was immersed in a 2% by mass aqueous solution of(3-acryloyloxypropyl)trimethoxysilane containing 2% by mass of aceticacid for 10 minutes, taken out and dried for 24 hours. The guide wirewas then washed with acetone. The treated SUS guide wire was immersed ina 1% by mass solution of benzophenone in acetone, taken out and dried.

The dried SUS guide wire was put in a glass vessel containing an aqueoussolution containing acrylic acid and potassium chloride adjusted atconcentrations of 2.5 M and 0.75 M, respectively, and the vessel wassealed with a stopper. After argon substitution was performed for twohours to remove oxygen, the glass vessel was irradiated with LED-UV (5mW/cm²) having a wavelength of 365 nm for 480 minutes while beingrotated, to cause surface-initiated radical polymerization.

Subsequently, the surface was washed with water and dried, and then theguide wire was immersed in a 1% by mass solution of benzophenone inacetone, taken out and dried.

The dried guide wire was put in a glass vessel containing an aqueoussolution of 2-(methacroyloxy)ethyl trimethylammonium chloride (1.25 M)containing potassium chloride adjusted at a concentration of 0.75 M, andthe vessel was sealed with a stopper. After argon substitution wasperformed for two hours to remove oxygen, the glass vessel wasirradiated with LED-UV (5 mW/cm²) having a wavelength of 365 nm for 960minutes while being rotated, to cause surface-initiated radicalpolymerization. Subsequently, the surface was washed with water to washaway unreacted monomer and the like. In this manner, a surface-modifiedmetal was prepared.

Example 7

The surface of a SUS guide wire (core wire) was washed with acetone anddried.

The guide wire was immersed in a 2% by mass aqueous solution of(3-acryloyloxypropyl)trimethoxysilane containing 2% by mass of aceticacid for 10 minutes, taken out and dried for 24 hours. The guide wirewas then washed with acetone. The treated SUS guide wire was immersed ina 1% by mass solution of benzophenone in acetone, taken out and dried.

The dried SUS guide wire was put in a glass vessel containing an aqueoussolution containing acrylamide and sodium chloride adjusted atconcentrations of 2.5 M and 1.5 M, respectively, and the vessel wassealed with a stopper. After argon substitution was performed for twohours to remove oxygen, the glass vessel was irradiated with LED-UV (5mW/cm²) having a wavelength of 365 nm for 800 minutes while beingrotated, to cause surface-initiated radical polymerization.

Subsequently, the surface was washed with water and dried, and then theguide wire was immersed in a 1% by mass solution of benzophenone inacetone, taken out and dried.

The dried guide wire was put in a glass vessel containing an aqueoussolution of 2-(methacroyloxy)ethyl trimethylammonium chloride (1.25 M)containing sodium chloride adjusted at a concentration of 1.5 M, and thevessel was sealed with a stopper. After argon substitution was performedfor two hours to remove oxygen, the glass vessel was irradiated withLED-UV (5 mW/cm²) having a wavelength of 365 nm for 480 minutes whilebeing rotated, to cause surface-initiated radical polymerization.Subsequently, the surface was washed with water to wash away unreactedmonomer and the like. In this manner, a surface-modified metal wasprepared.

Example 8

A surface-modified metal was prepared in the same manner as in Example5, except that the monomer used in the second polymerization was changedfrom the aqueous solution of 2-(methacroyloxy) ethyl trimethylammoniumchloride (1.25 M) to an aqueous solution of potassium 3-sulfopropylmethacrylate (1.25 M), and the duration of irradiation with LED-UV (5mW/cm²) having a wavelength of 365 nm was changed from 480 minutes to720 minutes.

Example 9

A surface-modified metal was prepared in the same manner as in Example8, except that the monomer used in the second polymerization was changedfrom the aqueous solution of potassium 3-sulfopropyl methacrylate (1.25M) to an aqueous solution of 2-methacryloyloxyethyl phosphorylcholine(1.25 M).

Example 10

A surface-modified metal was prepared in the same manner as in Example8, except that the monomer used in the second polymerization was changedfrom the aqueous solution of potassium 3-sulfopropyl methacrylate (1.25M) to [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)aminiumhydroxide (1.25 M).

Example 11

The surface of a SUS flat plate (10 cm square, 1 mm in thickness) waswashed with acetone and dried.

The plate was immersed in a 2% by mass aqueous solution of(3-acryloyloxypropyl)trimethoxysilane containing 2% by mass of aceticacid for 10 minutes, taken out and dried for 24 hours. The plate wasthen washed with acetone.

On the surface of the dried SUS plate was dropped an aqueous solution of2-(methacroyloxy)ethyl trimethylammonium chloride (1.25 M) containingsodium chloride and benzophenone adjusted at concentrations of 1.5 M and0.003 M, respectively. Then, the surface was covered with a 1 mm thickglass plate, and the covered surface was irradiated with LED-UV (5mW/cm²) having a wavelength of 365 nm for 180 minutes to causesurface-initiated radical polymerization. Subsequently, the surface waswashed with water to wash away unreacted monomer and the like. In thismanner, a surface-modified metal was prepared.

Comparative Example 1

The surface of a SUS flat plate (10 cm square, 1 mm in thickness) waswashed with acetone and dried before use.

Comparative Example 2

A SUS guide wire (core wire) was washed with acetone and dried beforeuse.

Comparative Example 3

A nickel-titanium alloy guide wire (core wire) was washed with acetoneand dried before use.

Comparative Example 4

The surface of a SUS flat plate (10 cm square, 1 mm in thickness) waswashed with acetone and dried.

The plate was immersed in a 2% by mass aqueous solution of(3-acryloyloxypropyl)trimethoxysilane containing 2% by mass of aceticacid for 10 minutes, taken out and dried for 24 hours. The plate wasthen washed with acetone. The treated SUS plate was immersed in a 1% bymass solution of benzophenone in acetone, taken out and dried.

On the surface of the dried SUS plate was dropped an aqueous solution of2-(methacroyloxy) ethyl trimethylammonium chloride (1.25 M). Then, thesurface was covered with a 1 mm thick glass plate, and the coveredsurface was irradiated with LED-UV (5 mW/cm²) having a wavelength of 365nm for 360 minutes to cause surface-initiated radical polymerization.Subsequently, the surface was washed with water to wash away unreactedmonomer and the like. In this manner, a surface-modified metal wasprepared.

Comparative Example 5

The surface of a SUS guide wire (core wire) was washed with acetone anddried.

The guide wire was immersed in a 2% by mass aqueous solution of(3-acryloyloxypropyl)trimethoxysilane containing 2% by mass of aceticacid for 10 minutes, taken out and dried for 24 hours. The guide wirewas then washed with acetone. The treated SUS guide wire was immersed ina 1% by mass solution of benzophenone in acetone, taken out and dried.

The resulting SUS guide wire was put in a glass vessel containing anaqueous solution of acrylic acid (2.5 M), and the vessel was sealed witha stopper. After argon substitution was performed for two hours toremove oxygen, the glass vessel was irradiated with LED-UV (5 mW/cm²)having a wavelength of 365 nm for 2,880 minutes while being rotated, tocause surface-initiated radical polymerization.

Subsequently, the surface was washed with water and dried, and then theguide wire was immersed in a 1% by mass solution of benzophenone inacetone, taken out and dried.

The dried guide wire was put in a glass vessel containing an aqueoussolution of 2-(methacroyloxy)ethyl trimethylammonium chloride (1.25 M),and the vessel was sealed with a stopper. After argon substitution wasperformed for two hours to remove oxygen, the glass vessel wasirradiated with LED-UV (5 mW/cm²) having a wavelength of 365 nm for2,880 minutes while being rotated, to cause surface-initiated radicalpolymerization. Subsequently, the surface was washed with water to washaway unreacted monomer and the like. In this manner, a surface-modifiedmetal was prepared.

Comparative Example 6

The surface of a SUS flat plate (10 cm square, 1 mm in thickness) waswashed with acetone and dried.

The plate was immersed in a 2% by mass aqueous solution of(3-acryloyloxypropyl)trimethoxysilane containing 2% by mass of aceticacid for 10 minutes, taken out and dried for 24 hours. The plate wasthen washed with acetone.

On the surface of the dried SUS plate was dropped an aqueous solution of2-(methacroyloxy) ethyl trimethylammonium chloride (1.25 M) containingbenzophenone adjusted at a concentration of 0.003 M. Then, the surfacewas covered with a 1 mm thick glass plate, and the covered surface wasirradiated with LED-UV (5 mW/cm²) having a wavelength of 365 nm for 180minutes to cause surface-initiated radical polymerization.

Subsequently, the surface was washed with water to wash away unreactedmonomer and the like. In this manner, a surface-modified metal wasprepared.

The surface-modified metals, flat plates, and guide wires were evaluatedfor sliding properties in the following way.

<Evaluation of Sliding Properties>

The surface-modified metals, flat plates, and guide wires were wateredand rubbed by a hand to subjectively evaluate sliding properties.

(Evaluation Results)

The surfaces of Comparative Examples 1, 2, and 3 were found not to beslippery but to have a feel like their original metal surface and thushave low sliding properties. In contrast, the surfaces of Examples 1 to4, and 11 were slippery and had significantly improved slidingproperties. The surfaces of Comparative Examples 4 to 6 were slipperybut less slippery than the surfaces of Examples 1, 6, and 11,respectively. The surfaces of Examples 5 to 7 were more slippery thanthe surface of Example 3. The surfaces of Examples 8 to 10 were asslippery as the surface of Example 5.

In addition, the surfaces of Examples 1 to 11 remained slippery andshowed no change in sliding properties after rubbing 100 times by ahand. These results demonstrate that the surface-modified metals of theexamples have good sliding properties (lubricity) and further haveexcellent durable sliding properties.

The invention claimed is:
 1. A surface-modified metal, at leastpartially having a treated surface, the treated surface being obtainedby treating a surface of a metal with a silane coupling agent, followedby adsorbing a hydrogen abstraction type photopolymerization initiatoronto the surface and then polymerizing a monomer in the presence of analkali metal salt.
 2. The surface-modified metal according to claim 1,wherein the treated surface is obtained by, after adsorbing the hydrogenabstraction type photopolymerization initiator onto the surface and thenpolymerizing the monomer in the presence of the alkali metal salt,further performing the following step at least once: polymerizing amonomer in the presence of a hydrogen abstraction typephotopolymerization initiator and an alkali metal salt; or adsorbing ahydrogen abstraction type photopolymerization initiator onto the surfaceand then polymerizing a monomer in the presence of an alkali metal salt.3. A surface-modified metal, at least partially having a treatedsurface, the treated surface being obtained by treating a surface of ametal with a silane coupling agent, followed by polymerizing a monomerin the presence of a hydrogen abstraction type photopolymerizationinitiator and an alkali metal salt.
 4. The surface-modified metalaccording to claim 3, wherein the treated surface is obtained by, afterpolymerizing the monomer in the presence of the hydrogen abstractiontype photopolymerization initiator and the alkali metal salt, furtherperforming the following step at least once: polymerizing a monomer inthe presence of a hydrogen abstraction type photopolymerizationinitiator and an alkali metal salt; or adsorbing a hydrogen abstractiontype photopolymerization initiator onto the surface and thenpolymerizing a monomer in the presence of an alkali metal salt.
 5. Thesurface-modified metal according to claim 1, wherein the monomer is atleast one selected from the group consisting of hydrophilic monomers,alkali metal-containing monomers, and halogen-containing monomers. 6.The surface-modified metal according to claim 1, wherein the silanecoupling agent is a vinyl group-containing compound.
 7. Thesurface-modified metal according to claim 1, wherein the metal to betreated is stainless steel or a nickel-titanium alloy.
 8. A medicaldevice, comprising the surface-modified metal according to claim
 1. 9.The medical device according to claim 8, which is a guide wire, asyringe needle, or a tube of a medical instrument.
 10. A method formodifying a metal surface, the method comprising: step 1 of treating ametal surface with a silane coupling agent; step 2 of adsorbing ahydrogen abstraction type photopolymerization initiator onto the metalsurface treated in the step 1 to form polymerization initiation points;and step 3 of polymerizing a monomer starting from the polymerizationinitiation points in the presence of an alkali metal salt to growpolymer chains on the metal surface.
 11. A method for modifying a metalsurface, the method comprising: step I of treating a metal surface witha silane coupling agent; and step II of polymerizing a monomer in thepresence of a hydrogen abstraction type photopolymerization initiatorand an alkali metal salt on the metal surface treated in the step I togrow polymer chains on the metal surface.
 12. The method according toclaim 10, wherein after the step 3, the method comprises performing, atleast once: a step of adsorbing a hydrogen abstraction typephotopolymerization initiator onto the surface and then polymerizing amonomer in the presence of an alkali metal salt; or a step ofpolymerizing a monomer in the presence of a hydrogen abstraction typephotopolymerization initiator and an alkali metal salt.
 13. The methodaccording to claim 11, wherein after the step II, the method comprisesperforming, at least once: a step of adsorbing a hydrogen abstractiontype photopolymerization initiator onto the surface and thenpolymerizing a monomer in the presence of an alkali metal salt; or astep of polymerizing a monomer in the presence of a hydrogen abstractiontype photopolymerization initiator and an alkali metal salt.